This application discloses a high solidity axial fan and a method of assembling the high solidity axial fan.
Typically, furnaces, air conditioners, air handlers and fan coil units utilize forward curved fans. Forward curved fans are much more costly to manufacture than a vane axial fan. Vane type axial fans have been used to replace the forward curved fans in many of these applications to take advantage of the cost savings. However, a vane axial fan is limited in applications due to poor stall characteristics. Stall is a phenomenon that occurs during specific flow conditions that causes partial flow reversal within the blade passage. Specifically, stall occurs when an angle between the fan blade and the incoming air flow is too steep causing a rise in static pressure across the fan blade typically when flow is reduced below the intended design point.
Increasing fan speed can offset the poor stall characteristics of axial fans. However, increasing fan speed results in a corresponding increase in noise. It is always desirable to have as little noise as possible for residential application such as furnaces and air conditioners.
A known method of preventing stall is to vary the angle and speed of the fan blades relative to air flow. Such systems are prohibitively expensive due to the control systems and mechanisms necessary to continually adjust the angle and speed of the fan blades and speed. Another method or preventing stall includes increasing the solidity of the fan. Solidity is the ratio of fan blade area to the swept area of the fan. Increasing fan solidity prevents stall by spreading the force differential between incoming air and outgoing air over a larger area, reducing the difference in pressure between the upper and lower surfaces of the fan blade to reduce tip leakage. High solidity also reduces the pressure gradient from the inlet of the fan blade to the trailing edge of the blade, and thus the possibility of flow separation. Further, a fan having high solidity can move the same amount of air with less blade pitch, which in turn prevents or improves stall characteristics. Improvements gained by increasing fan solidity are well known in the art.
A high solidity axial fan can be constructed by overlapping the fan blades, to increase the area of the fan blades relative to the swept area of the fan. However, manufacture of a high solidity fan is very difficult and cost prohibitive. Further, a fan constructed by plastic injection molding techniques would required a complex and prohibitively costly mold tool to mold overlapping fan blades.
For these reasons it is desirable to provide a method of constructing and assembling an axial vane fan having high solidity to improved stall properties such that the axial vane fan may be run at a reduced speed, thereby reducing noise, and making a vane type axial fan commercially feasible for use in residential applications.
The invention is a method of assembling a vane axial fan having high solidity to improve stall properties such that the vane axial fan may be run at reduced speeds, thereby reducing noise output.
The subject invention overcomes the problems of prior art vane axial fans by providing a two-piece axial fan assembly provides for the fan blades to be overlapped to increase solidity. The method of fabricating the vane axial fan of this invention includes, providing a first plurality of fan blades attached to a first hub, providing a second plurality of fan blades attached to a second hub, interfitting the second plurality of fan blades between the first plurality of fan blades and interlocking the second hub onto the first hub.
The method of assembling a vane axial fan provides a method of constructing and assembling an axial fan having high solidity to improved stall properties such that the axial fan may be run at a reduced speed, thereby reducing noise, and making a vane axial fan commercially feasible for use in applications requiring low noise emission.